Electron beam irradiation apparatuses mostly use monitoring devices to check electron beam irradiation state for uniform irradiation of target objects for correct sterilization.
As a conventional art for keeping track of state of electron beam irradiation, JP 08-265738 A1 (Patent Literature 1) has described an invention, in which lights emitted on irradiation of an irradiation target with electron beam is photographed and the photographed lights are image processed for its intensity distribution to see the electron beam irradiation state.
As an art that decides abnormality in the electron beam irradiation state by detecting broken filament, JP 11-84099 A1 (Patent Literature 2) has described an invention, in which plural filaments grouped into two are arranged so that direction of current flow through each group will be mutually opposite and the difference between these currents is measured with a current transformer checking for balancing state of currents; and thereby the state is judged to be broken filament in the event when the current balance is lost.
Further, JP 08-313700 A1 (Patent Literature 3) has described another invention for an electron beam source. The invented electron beam source has a state detector that detects temperature of the irradiation window thereof while the source is in operation. The life of an irradiation window is diagnosed based on the data of the state of the irradiation window loaded by the state detector. Information derived from the detected temperature rise and temperature distribution of the irradiation window to track the dose and irradiation distribution of the electron beam is fed-back to the electron gun control circuit and electromagnet for regulating irradiation area through a feedback circuitry to permit the electron beam source to keep running within the tolerance free from the breakage of the irradiation window.
In addition to the above, an invention for a method of deciding the abnormality in an image processing system has been described in JP 2005-121925 A1 (Patent Literature 4). In the invented method, image data is binarized into a bright part and a dark part and into which range among the plural ranges of threshold values the luminance of a specific position falls is examined to decide the cause of the abnormality in the illumination lighting source or imaging apparatus of the image processing system.
Although the art defined in Patent Literature 1 judges whether the electron beam irradiation is normal or abnormal, features related to determination of cause of abnormality when the electron beam irradiation is judged abnormal is not disclosed. For example, how to decide whether the abnormality is caused from either the broken filament or attributable to the vacuum window is not disclosed. Therefore, when the state is judged abnormal in the art defined in Patent Literature 1, the operation of the electron beam irradiation equipment must be stopped to undergo checking all the abnormality-questionable sections before resuming operation. This means it is likely that the checking will consume much time.
With the art defined in Patent Literature 2, the broken filament is detected instantly. However, the Literature does not disclose features related to detection of abnormality due to unusualness of the vacuum window or axis deviation. This means that detection of electron beam irradiation abnormality is difficult in the art defined in Patent Literature 2 even though unusualness of the vacuum window or axis deviation occurs, unless the broken filaments; and consequently that the irradiation target is likely to finish sterilization process without knowing dose is insufficient.
The art defined in Patent Literature 3 diagnose the life of an irradiation window based on the temperature rise and temperature distribution thereof derived from the measurements of the temperature of the irradiation window. This means that the art does not consider any cause of abnormality attributable to those other than the irradiation window, although the abnormality of the irradiation window can be detected. To enable decision of causes of abnormality resulted from broken filament or axis deviation, it is necessary to provide another detector for such purpose separately. Therefore, a system by the art has involved such a problem that rigging additional detector may invite an anxiety of the system being complicated.
The art defined in Patent Literature 4 decides the cause of abnormality by applying threshold value processing to the image data, in which the determination handles abnormalities of the lights source lamp for illuminating imaging objects and the imaging apparatus. Therefore, the art is not such a technique as observes luminance of lights emitted from an object under irradiation with electron beam, performs threshold value processing, and decides the cause of the abnormality in the state of the electron beam irradiation. In other words, the defined art does not specifically identify which section of the electron beam irradiation means has the cause of the abnormality.
In view of above stated problems, the present invention aims to provide an electron beam irradiating apparatus with monitoring device. The invented apparatus is capable of not only deciding whether the electron beam irradiation is normal or abnormal but also identifying the causes of abnormalities when occurred; the apparatus thereby shortens the time required to perform a check operation. The apparatus is further capable of deciding the causes for plural abnormalities with single device relying on luminance of images stored in a storage means.